1. Field of the Invention
The present invention relates to a switch device used as a power switch of an electronic device, and more particularly, to the structure of a quick-acting switch device in which contacts are opened and closed by using the inversion of a spring.
2. Description of the Related Art
The structure of a conventional quick-acting switch device is shown in FIGS. 13 to 15. FIG. 13 is a longitudinal sectional view showing an OFF state of the switch device. FIG. 14 is a longitudinal sectional view showing an ON state of the switch device. FIG. 15 is a partial explanatory view of a contact mechanism section.
The illustrated conventional switch device principally includes a casing 21 made of an insulating material, such as a synthetic resin. A fixed terminal 22 is placed on the inner bottom surface of the casing 21 and has a fixed contact 22a on its upper surface. A center terminal 23 is similarly placed on the inner bottom surface of the casing 21 adjacent to the fixed terminal 22. A conductor plate 28 is movably supported by the center terminal 23 and has at one end a movable contact 29 that is movable closer to and further apart from the fixed terminal 22. A support plate 27 is retained by the conductor plate 28 and the center terminal 23 so as to movably support the conductor plate 28, a leaf spring 30 retained in a bent form between the conductor plate 28 and the center terminal 23 so as to move the conductor plate 28 by its bending and stretching motions, and a slide member 31 for moving a projection 30a of the leaf spring 30 in contact therewith so as to shift the conductor plate 28 closer to and further apart from the fixed terminal 22.
The center terminal 23 is made of a conductive metal plate or the like, and includes a support plate retaining projection 23a for retaining the support plate 27 and a leaf spring retaining projection 23b for retaining the leaf spring 30. The support plate retaining projection 23a and the leaf spring retaining projection 23b have, respectively, retaining V-grooves 23c and 23d formed nearly opposed to each other. The support plate 27 and the leaf spring 30 are retained at one end by the retaining groves 23c and 23d respectively.
The support plate 27 is similarly made of a conductive metal plate, is substantially U-shaped, and has an opening at the center where the leaf spring retaining projection 23b can be loosely fitted. The support plate 27 is retained by the retaining V-groove 23c of the support plate retaining projection 23a at one end, and is retained adjacent to the side of the conductor plate 28, where the movable contact 29 is attached, at the other end.
The conductor plate 28 is similarly made of a conductive metal plate, and has at its center an opening where the support plate retaining projection 23a and the leaf spring retaining projection 23b can be loosely fitted, and the movable contact 29 at one end. The conductor plate 28 is movably mounted on the center terminal 23 while one end of the support plate 27 is retained at one inner end of the opening, and the other end of the opening is retained by the leaf spring 30.
The leaf spring 30 is made of an elastic thin metal plate, and is substantially V-shaped. One end of the leaf spring 30 is retained by the retaining V-groove 23d of the leaf spring retaining projection 23b of the center terminal 23, and the other end thereof is retained on the inner side of the opening of the conductor plate 28 opposite from the side where the support plate 27 is retained. The leaf spring 30 is placed in a bent form between the center terminal 23 and the conductor plate 28. Adjacent to the top of the nearly V-shaped leaf spring 30, an operating projection 30a is formed so as to drive the conductor plate 28 when the slide member 31 slides.
In order to assemble the contact mechanism of the above-described switch device, since the conductor plate 28 is movably mounted on the center terminal 23, the leaf spring 30 must be placed in a bent form between one inner end of the opening of the conductor plate 28 and the leaf spring retaining projection 23b of the center terminal 23 in a state in which one end of the support plate 27 is retained at the other inner end of the opening of the conductor plate 28, and the other end of the support plate 27 is retained by the support plate retaining projection 23a of the center terminal 23. In this case, since the leaf spring 30 is mounted in an elastically bent form between the conductor plate 28 and the center terminal 23 with the support plate 27 therebetween, the conductor plate 28, the support plate 27, and the leaf spring 30 are movably mounted together on the center terminal 23.
The operation of the above switch device will now be described. When the slide member 31 is pressed, it slides in the pressing direction (rightward in the figure) and presses the adjacency of the top of the V-shaped leaf spring 30, and the leaf spring 30 is pivoted clockwise on the retaining V-groove 23d of the leaf spring retaining projection 23b of the center terminal 23. In this case, the conductor plate 28 is turned downward together with the support plate 27 on the retaining V-groove 23c of the support plate retaining projection 23a of the center terminal 23. When the retaining portion between the conductor plate 28 and the leaf spring 30 passes over the retaining V-groove 23c (the point of inversion of the leaf spring 30), the conductor plate 28 moves downward and the movable contact 29 contacts the fixed contact 22a, thereby closing the circuit. In this case, the slide member 31 is locked in a pressed position.
When the slide member 31 is further pressed in this state, it is unlocked and returned by the urging force of the return spring 26 in a direction (leftward in the figure) opposite from the pressing direction. In this case, when the operating projection 30a of the leaf spring 30 is pressed, and the leaf spring 30 is pivoted counterclockwise and passes through the point of inversion, the conductor plate 28 moves upward, and the movable contact 29 separates from the fixed contact 22a, thereby opening the circuit.
In the above-described conventional switch device, the leaf spring 30 is used in order to move the conductor plate 28 and, at the inversion of leaf spring 30, to establish a contact between the movable contact 29 and the fixed contact 22a. However, since the required load is heavy, the leaf spring 30 must be made of a spring material with a great allowable stress (for example, titanium copper or beryllium copper). This makes it difficult to maintain machinablility and dimensional accuracy, and increases the parts cost.
Furthermore, since the support plate 27 and the leaf spring 30 are made of a platelike material, the shape is complicated, and the material yield is low. Since the support plate 27 and the leaf spring 30 contact with the center terminal 23 at cut edge portions, they are prone to wear, and the reliability of the contact portion is decreased.
The present invention has been made in order to overcome the above problems, and an object of the invention is to provide a quick-acting switch device in which machinablility and dimensional accuracy can be easily maintained the cost can be reduced, and the reliability of the contact portion can be improved by making a spring member of a contact mechanism of a round wire.
In order to achieve the above object, according to an aspect of the present invention, there is provided a switch device including a fixed contact, a conductor plate having a movable contact which is moved closer to and further apart from the fixed contact, a center terminal for movably supporting the conductor plate, a support arm retained by the conductor plate at one end and retained by the center terminal at the other end, a spring member placed in a bent form between the conductor plate and the center terminal so as to movably support the conductor plate on the center terminal in cooperation with the support arm, and a slide member for moving the movable contact closer to and further apart from the fixed contact by shifting the conductor plate in a direction nearly perpendicular to the sliding direction by the elastic force of the spring member, wherein the support arm and the spring member are made of an elastic wire, and portions of the support arm and the spring member retained by the conductor plate and the center terminal are formed of arc-shaped surfaces.
In this case, the shape is simplified, the material yield is improved, and machinablility and dimensional accuracy can be maintained easily. Moreover, since the support arm and the spring member are retained by the conductor plate and the center terminal on the arc-shaped surfaces, they are less subject to wear, and the reliability of the contact portion is improved.
Preferably, the support arm has a pair of opposing flexible arm pieces, and the arm pieces are elastically urged toward side walls of the conductor plate.
In this case, a reliable contact can be established between the support arm and the conductor plate, and the conductor plate and the center terminal will not be disconnected due to bounce or chattering when the contacts are opened and closed. This improves the reliability of the contact.
Preferably, each of the side wall has a regulating projection with an inclined surface, and the arm pieces are put into elastic contact with the inclined surfaces when the conductor plate shifts in the direction perpendicular to the sliding direction and the movable contact moves in such a direction as to contact with the fixed contact.
In this case, since the elastic contact pressure between the arm pieces and the inclined surfaces is increased with the movement of the conductor plate toward the fixed contact, the reliability of the contact is improved further.
Preferably, the spring member is formed of a helical torsion spring.
In this case, the shape is simplified, machinablility and dimensional accuracy can be easily maintained, and the cost can be reduced, compared with a case in which a leaf spring or the like is formed by press-molding a metal plate. Furthermore, since the spring member is made of a round wire of circular cross section, it is engaged with the center terminal and the conductor plate on the conductor plate""s arc-shaped surfaces. Therefore, smooth sliding is possible, scraping or the like are avoided, and the reliability of the contact is improved.
Preferably, the slide member has an operating face portion formed of an inclined surface, the conductor plate has a contact portion to be contacted with the operating face portion, and the operating face portion slides in contact with the contact portion with the sliding of the slide member so as to shift the conductor plate in the direction nearly perpendicular to the sliding direction. This reduces the size and thickness of the switch device.
Further objects, features, and advantages of the present invention will become apparent from the following description of the preferred embodiments with reference to the attached drawings.